The present invention relates to the discharge of molten metal from a casting ladle or the like under exclusion of slag. The invention also relates to a method and equipment for slag-free removing molten metal from a ladle or other vessel having a bottom tap; the molten metal in the ladle being covered by a slag layer.
Discharging a ladle or any other metallurgical vessel in general requires that as early as possible the discharge of the slag together with molten metal be avoided. Of course in the case of a bottom tap for metal discharge generally there will be slag-free metal for a long time that flows out of the tap, but owing to various processes inside the ladle slag particles may at a fairly early time be sucked in and drawn into the outflow of the molten metal, and that is to be prevented. Optically recognizing the point in time when slag tends to be also discharged through the bottom tap is quite difficult since the slag will be sucked into an eddy; the slag moves actually in the interior of such an eddy. While an eddy can be recognized, it is difficult to determine at what point in time slag is actually sucked into the interior of the casting stream and eddy. The slag is usually visible when in the case of regular or continuous casting, slag provides precipitate again either on the top part of the casting or e.g. in the tundish that feeds the mold for continuous casting.
The slag location has been determined, for example, by means of electrically inductive measuring methods using the difference in electrical conductivity of metal and of slag, particularly in the stream of pouring metal. While technically quite adequate, the expenditure for the requisite equipment is too large and still the measuring result is not that accurate. German Pat. No. 28 14 699 proposes in the alternative to recognize the inclusion of slag by means of gravimetric methods.